Ergonomics also called human factors is an applied science that makes the user central to design by improving the fit between that user and his or her tools, equipment, and environment..
Trang 115.1 ERGONOMICS
A widespread increase in the availability of technology in the second half of the twentieth century has meant that more and more people come in contact with a variety of product designs on a daily basis Regardless of this increase in the number and types of human users, many engineers still concentrate their design efforts on the machine or system alone, forcing the user to adjust to fit the product Such readjustments on the part of the user can lead to discomfort and dissatisfaction with the design, as well as more serious effects, such as safety hazards and personal injury
Ergonomics (also called human factors) is an applied science that makes the user central to design
by improving the fit between that user and his or her tools, equipment, and environment Key here
is that designs are developed to fit both the physiological and psychological needs of the user Ergonomists examine all ranges of the human interface, from static anthropometric measures and movement ranges to users' perceptions of a product This interface involves both software (displays, electronic controls, etc.) and hardware (knobs, grips, physical configurations, etc.) issues
Ergonomics grew into a distinct scientific discipline during the second world war What began as
a form of engineering (human engineering or human factors engineering) has come to encompass a wide range of interdisciplinary professions, including psychology, industrial design, medicine, and computer science Its practitioners' range in focus includes concept modeling and product design, job performance analysis, functional analysis, workspace and equipment design, computer interfaces, environment design, and so forth
15.2 HUMANPERFORMANCE
The true basis of ergonomics is understanding the limitations of human performance capabilities relative to product interaction These limitations are either physical or cognitive/perceptual in nature, but all address how people respond to man-made designs Such interface analysis is crucial to estab-lishing a safe and effective system of operation or environment for the user
Mechanical Engineers' Handbook, 2nd ed., Edited by Myer Kutz.
ISBN 0-471-13007-9 © 1998 John Wiley & Sons, Inc
CHAPTER 15
ERGONOMIC FACTORS IN DESIGN
Bryce G Rutter, Ph.D., Principal
Anne Marie Becka, Editor
Metaphase Design Group, Inc.
St Louis, Missouri
15.1 ERGONOMICS 329
15.2 HUMANPERFORMANCE 329
15.2.1 Physical Ergonomics 330
15.2.2 Perceptual and Cognitive
Ergonomics 330
15.3 THE DESIGN PROCESS 330
15.4 DESIGNRESEARCH 331
15.5 ERGONOMICANALYSES 332
15.5.1 Anatomical Analysis 332
15.5.2 Biomechanical Analysis 333
15.5.3 Task Analysis 335
15.5.4 Link Analysis 335
15.5.5 Motion Analysis 335 15.5.6 Thermographic Imprint
Analysis 336 15.5.7 Low-Speed Cine Analysis 336
15.6 DESIGNRESEARCH METHODS 336
15.6.1 Competitive Product Analysis 336 15.6.2 Product Performance
Analysis 336 15.6.3 Usability Studies 336
15.7 COST-BENEFIT ANALYSIS OF ERGONOMICS AND DESIGN RESEARCH 337
Trang 2Fig 15.1 General interdisciplinary nature of human factors with selected
examples (from Ref 1, p 90 Reprinted by permission).
15.2.1 Physical Ergonomics
A thorough understanding of the physical characteristics of a wide range of people is essential to any product that is designed for human use When analyzing design relative to human performance, ergonomists study static anthropometric data, which includes sizing percentiles (e.g., lengths, mea-surements) of a wide range of populations, including gender, age, race, and other such factors Ranges
of joint motions, strengths, and grips for varying human percentiles are also reviewed These data serve as valuable information to designers and help ensure the final product will physically fit the targeted end-user, be it a child, the aged, or a particular racial population, and so forth
15.2.2 Perceptual and Cognitive Ergonomics
Proper fit of a product to a user does not end with the physical interface The perceptual and cognitive demands a product places on a user must also be examined Note that a great misconception under-lying these capabilities is that they address emotive responses of the user However, neither are qualitative findings; both types offer fact-based, quantitative data to be used in product development Perceptual responses are those filtered through one or more of the five senses, such as tactile and auditory feedback of controls Cognitive responses are based on logic, reason, and how users process information Cognitive issues include intuitiveness of control features and functions as well as icon representation and label comprehension
15.3 THE DESIGN PROCESS
Implementing an ergonomics program can help ensure a product's successful transition from the drawing board to the end-user However, human factors cannot be examined in a vacuum Ergonomists must work directly with designers and engineers throughout the entire design development process, each providing feedback to the other during concept development and testing In addition to standard ergonomic analyses, design research should be conducted with targeted end-users to identify design problems that are often overlooked by the engineer, who examines the product only within the design environment Such end-user research serves to measure a design's overall efficacy on a wide range
Trang 3^Adapted from U.S Army data reported by Gordon et al (1989) (from K Kroemer, H Kroemer,
and K Kroemer-Elbert, Ergonomics: How to Design for Ease and Efficiency, p 30 ©1994 Reprinted
by permission of Prentice-Hall, Englewood Cliffs, NJ)
b Estimated
Note: In this table, the entries in the 50th percentile column are actually "mean" (average) values.
The 5th and 95th percentile values are from measured data, not calculated (except for weight) Thus, the values given may be slightly different from those obtained by subtracting 1.65 SD from the mean (50th) percentile, or by adding 1.65 SD to it
of user perception and knowledge levels Resulting data can provide a tangible starting point upon which design revisions or new product concepts can be made
15.4 DESIGNRESEARCH
A core component of a successful product design is understanding the wants and needs of the product's end-users Therefore, talking with target customers to gain insight into their requirements
is a logical step in concept development Unfortunately, most manufacturers and engineers approach this issue through "gut-feeling" guesswork — fabricating a list of items or issues based on the premonitions of the development team or head of manufacturing This method of design development
is doomed from its inception, as engineers and manufacturers are often so far removed from their
Table 15.1 Body Dimensions of U.S Civilian Adults, Female/Male, in cma
Heights
(f above floor, j above seat)
Stature ("height" K
Eye height /
Shoulder (acromial) height /
Elbow height7
Wrist height7
Crotch height7
Height (sitting)5
Eye height (sitting)5
Shoulder (acromial) height (sitting)7
Elbow height (sitting)*
Thigh height (sitting)5
Knee height (sitting) 7
Popliteal height (sitting) 7
Depths
Forward (thumbtip) reach
Buttock-knee distance (sitting)
Buttock-popliteal distance (sitting)
Elbow-fingertip distance
Chest depth
Breadths
Forearm-forearm breadth
Hip breadth (sitting)
Head Dimensions
Head circumference
Head breadth
Interpupillary breadth
Foot Dimensions
Foot length
Foot breadth
Lateral malleolus height7
Hand Dimensions
Circumference, metacarpale
Hand length
Hand breadth, metacarpale
Thumb breadth, interphalangeal
Weight (in kg)
Percentiles 5th 50th 95th SD
152.78/ 164.69 162.94/ 175.58 173.73/ 186.65 6.36/6.68 141.52/ 152.82 151.61/ 163.39 162.13/ 174.29 6.25/6.57 124.09/ 134.16 133.36/ 144.25 143.20/ 154.56 5.79/6.20 92.63/ 99.52 99.79/ 107.25 107.40/ 115.28 4.48/4.81 72.79/ 77.79 79.03/ 84.65 85.51/ 91.52 3.86/4.15 70.02/ 76.44 77.14/ 83.72 84.58/ 91.64 4.41/4.62 79.53/ 85.45 85.20/ 91.39 91.02/ 97.19 3.49/3.56 68.46/ 73.50 73.87/ 79.20 79.43/ 84.80 3.32/3.42 50.91/ 54.85 55.55/ 59.78 60.36/ 64.63 2.86/2.96 17.57/ 18.41 22.05/ 23.06 26.44/ 27.37 2.68/2.72 14.04/ 14.86 15.89/ 16.82 18.02/ 18.99 1.21/1.26 47.40/ 51.44 51.54/ 55.88 56.02/ 60.57 2.63/2.79 35.13/ 39.46 38.94/ 43.41 42.94/ 47.63 2.37/2.49
67.67/ 73.92 73.46/ 80.08 79.67/ 86.70 3.64/3.92 54.21/ 56.90 58.89/ 61.64 63.98/ 66.74 2.96/2.99 44.00/ 45.81 48.17/ 50.04 52.77/ 54.55 2.66/2.66 40.62/ 44.79 44.29/ 48.40 48.25/ 52.42 2.34/2.33 20.86/ 20.96 23.94/ 24.32 27.78/ 28.04 2.11/2.15
41.47/ 47.74 46.85/ 54.61 52.84/ 62.06 3.47/4.36 34.25/ 32.87 38.45/ 36.68 43.22/ 41.16 2.72/2.52
52.25/ 54.27 54.62/ 56.77 57.05/ 59.35 1.46/1.54 13.66/ 14.31 14.44/ 15.17 15.27/ 16.08 0.49/0.54 5.66/ 5.88 6.23/ 6.47 6.85/ 7.10 0.36/0.37
22.44/ 24.88 24.44/ 26.97 26.46/ 29.20 1.22/1.31 8.16/ 9.23 8.97/ 10.06 9.78/ 10.95 0.49/0.53 5.23/ 5.84 6.06/ 6.71 6.97/ 7.64 0.53/0.55
17.25/ 19.85 18.62/ 21.38 20.03/ 23.03 0.85/0.97 16.50/ 17.87 18.05/ 19.38 19.69 21.06 0.97/0.98 7.34/ 8.36 7.94/ 9.04 8.56/ 9.76 0.38/0.42 1.86/ 2.19 2.07/ 2.41 2.29/ 2.65 0.13/0.14 39.2fc/ 57.7fc 62.01/ 78.49 84.8b/ 99.3fc 13.8fo/12.6b
Trang 4Other times, manufacturers circumvent actual end-user research in lieu of product assessment by their marketing department This form of "research" is extremely qualitative and often unsubstan-tiated by end-user feedback Worse yet is when manufacturers base product design requirements on results of a survey of sales personnel It is generally believed that because sales personnel are on the floor daily with customers, they have insight into customers' wants and needs However, such methods can be disastrous, as sales representatives are not trained to observe and categorize human behavior,
as many human factors specialists are
15.5 ERGONOMICANALYSES
Ergonomic assessments successfully define special requirements of unique user groups by providing
a comprehensive assessment of the degree of compatibility between the user, the product, and the user's workspace Data collected include empirical measures of workspace envelopes, task and link analyses (used to identify inefficiencies in the conduct of work, illogical procedures, and hazards), and definitions of anthropometric requirements (the dimensions of the human body) Several types
of ergonomic analyses are listed below
15.5.1 Anatomical Analysis
An anatomical analysis is the study of the interaction between a product and various anatomical features of the user's body (e.g., the musculoskeletal system, nerves, veins and arteries, joints, etc.) The goal of this analysis is to identify biological constraints for design that, if exceeded, may lead
to user discomfort, stress, strain, pain, or occupational disability Typically, a product's effect on the muscular, skeletal, nervous, and circulatory systems is explored
Design programs in which this type of analysis is especially important are those that involve large forces being exerted, rapidly repeating body motions, and/or high pressure on a portion of the user's anatomy An anatomical analysis allows ergonomists to identify potentially harmful effects of the use
SHOULDER Fig 15.2 Selected examples of range of joint motions: upper extremities (from B G Rutter,
Dynamic Anatomical Anthropometry ©1981 Reprinted by permission).
Trang 5FINGER FLEXION WRIST
Fig 15.2 (Continued).
of a product on its users It also provides design guidelines in the form of constraints on the user interface The various anatomical systems affect the level of anatomical analyses In addition, the type of product being designed and the nature of the interaction between the user and the product determine what anatomical features need to be considered in the analysis Such analysis is best when performed by someone trained in kinesiology (the study of human movement)
15.5.2 Biomechanical Analysis
Biomechanical analysis involves modeling the human body as a mechanical system The various measurement tools used in biomechanical analysis all provide information about the mechanics of the user's body when interacting with a product or performing a task Such analysis is appropriate when the goal is to quantitatively assess or validate the efficiency and/or safety of one or more
ELBOW/ SHOULDER
FLEXION
ABDUCTION
Trang 6HIP ROTATION ANKLE AND BIG TOE ROTATION Fig 15.3 Selected examples of range of joint motions: lower extremities, (from B G Rutter,
Dynamic Anatomical Anthropometry ©1981 Reprinted by permission).
products When precise measurements of the human interaction are required, a biomechanical analysis
is essential It provides quantitative measures of the patterns of muscular exertion and/or body position during actuation This information provides an indication of the biomechanical efficiency and safety of the product tested
Performing a biomechanical analysis using any of the four tools discussed below is a complex process requiring specialized equipment and personnel Various other biomechanical tools exist The following are the most commonly used
Force Sensors
For this type of analysis, force sensors/transducers are mounted on a product or a test subject Signals provide a sample force applied between the user and the test product Such analysis allows researchers
to develop a map of the distribution and range of forces involved in the use of a product If loading
is found to be too heavy in an area of the body that cannot handle such a load, designers know they must rework the concept design to ensure user comfort and safety
Force Plates
These sensing devices provide feedback to researchers on a user's center of gravity and sway/motion during product interaction Sensors takes sample measures of weights applied during different posi-tions of user activity These measures allow researchers to determine the activity's affect on a body
in order to determine possible stress, strain, fatigue, and injury to the user
Accelerometers
These devices measure the rate of movement change over time in order to determine user velocity during product use Sensors sample the range of acceleration of different parts of the user's body in order to determine overall movement rates Such data are critical in that it tells researchers how using different products affects users' movement (i.e., level of fatigue) over time
Data Glove
This research tool has sensors that measure the movement of a user's hand and all related digits during product operation The data collected allows researchers to track grip extents, various grip architects, grasping strategies, and the range of movement of the entire arm during product use Researchers analyze this information to determine whether a product will cause overextension, thereby causing pain and injury
ROTATION
in FLEXION
DORSIFlEXION
PLANTAR FLfXION
Trang 7Fig 15.4 Model of user interface issues: factors involved, (from Ref 2.
Reprinted by permission).
15.5.3 Task Analysis
Task analysis involves breaking a job function down into its constituent parts, assessing human resources and time requirements, then using the information to redesign the task to optimize user output The systematic breakdown of the individual tasks into sub-tasks allows a thorough review and the subsequent improvement of a product or system Task analysis has been applied to the assessment and redesign of products, industrial worksites, information displays, product control pan-els, architectural layouts, and so on It is most effective in the review of multisequential and/or complicated activities
15.5.4 Link Analysis
Link analysis is used to identify inefficiencies in time/motion paths of a user performing a task and details frequencies of such paths Time/motion analysis traces can be performed directly on photo-graphs of a task/product and can be recorded with a motion-detection system Results graphically illustrate the human interface and allow for the identification of inefficiencies and repetitive motions that are nonproductive or may lead to diminished productivity or injury Link analysis provides a graphic measure of the user interface and contributes a relatively quick yet precise evaluation of the path of human interaction with a product or system
15.5.5 Motion Analysis
This assessment method determines the kinematics (measurements of the space/time attributes of human movement) of the user interface Motion analysis provides a detailed quantitative profile of a movement required for a particular product-related activity Such analysis provides a detailed quan-titative assessment of a product's efficiency, consistency, and safety
Trang 815.5.6 Thermographic Imprint Analysis
Thermographic imprints are used to analyze the physical interaction between a product and its user For this study, a product or concept design is treated with a heat-sensitive paint system that changes color when in contact with heat from the user's body The result is a visual thermographic imprint that illustrates patterns of contact between the user and product that are not readily available from photographs or videotape This form of analysis is useful in diagnosing potential interface problems, such as excessive contact areas, accidental activation of controls, and pressure on sensitive anatomical features
15.5.7 Low-Speed Cine Analysis
Low-speed cine analysis involves analyzing videotape frame by frame using an image capture system This technique is especially useful for exploring the kinematics of tasks/interfaces that either occur very quickly or are too complicated to follow through normal observation In addition, time/motion studies can be performed This analysis provides a detailed quantitative analysis of human movement that can be used to assess the efficiency, consistency, and safety of the user interface
15.6 DESIGN RESEARCH METHODS
Design research tools and techniques are often used in conjunction with various ergonomic analyses
in order to optimize a product's usability Both qualitative and quantitative tools are used to define user needs, product features and functionality, purchasing criteria, and end-user reactions to currently available products and new product concepts
It is important to differentiate the following forms of analyses from traditional market research Where methods of research such as focus groups serve to catalogue what customers do, design research goes one step further by analyzing why they respond as they do Design research tools have the ability to move beyond more shallow, traditional market research and allow researchers to discern patterns in seemingly chaotic customer behavior
15.6.1 Competitive Product Analysis
Competitive product analysis provides a systematic evaluation of competitive product performance, design, ergonomics, safety, comfort, and other similar design factors It also provides comparative testing among products or product concepts to establish performance benchmarks and relative per-formance ratings Resulting quantitative data include function and feature analysis, assessment of fit and finish, assessment of assembly, appropriateness of materials and support manuals, effectiveness
of instruction guides, and statistical evaluations of the intuitiveness of controls and interface logic Competitive product analysis can range from an internalized approach to a user-based treatise whose scope is determined by demographic guidelines
The exploratory nature of this form of research dictates that it be executed early in the product development process An abbreviated competitive product analysis with users can serve as a form of design validation after a product has been developed
15.6.2 Product Performance Analysis
This form of design research involves the quantitative testing and evaluation of a product's perform-ance attributes Techniques include on-site and laboratory measures relative to use efficiency, product efficacy, and safety, using various types of sensing technologies Depending upon the scope of inquiry and product/system being assessed, it may include motion analysis, biomechanical analysis, low-speed cine analysis, and so on Quantitative data resulting from these analyses include such mea-surements as error rates, reaction and response times, motion-velocity analysis, acceleration, jerk, and movement paths of body parts Qualitative evaluations, such as surveys, interviews, and observation, are also utilized
Product performance analysis provides the clearest and most quantified and qualified measure in the process of existing product, competitive product, mock-ups, or prototype assessment This design-research method can be used to establish industry benchmarks by ascertaining performance levels on
a currently marketed product or in the concept development phase to assist in the selection of the optimal design
15.6.3 Usability Studies
Usability studies provide both quantitative and qualitative information relative to the user's physical, cognitive, and perceptual relationship with the product Test subjects are allowed to interact with the product for a period of time in the environment in which the product would normally be used Researchers then interview users for a detailed understanding of the product's feature and functions, its ease of use, intuitiveness of operation, and so forth Perceptual and actual responses are measured
at various stages of product contact for an understanding of both the psychological and physiological interface
Trang 915.7 COST-BENEFIT ANALYSIS OF ERGONOMICS AND DESIGN RESEARCH
Numerous industry studies have clearly illustrated positive cost-benefit advantages of implementing ergonomic programs After all, what manufacturers cannot attest to some number of "No Problem Found" (NPF) returns of products? A buyer returns a product simply because it "does not work." Put simply, the product did not fit the user in some manner: perhaps it caused the user discomfort, perhaps he or she just could not figure out how to get the product to work, or perhaps the buyer thought the product was just too complicated or difficult to even try to use In all of these scenarios,
no fault can be found with the product or design except that it was developed without the user in mind
Bear in mind that the cost of corrections to a poorly designed product geometrically increases throughout the development process Therefore, human factors specialists should begin working with engineers and designers in the early stages of product development When ergonomists are called in
to fix a product that has already been sent to market and failed, costs will escalate
A manufacturer's decision to adopt an ergonomic orientation will serve to reposition its products from a commodity-based supplier to a supplier of high-value products Integrating ergonomics into
a design program ensures more comfortable, safe, and productive design solutions and a better overall product for the end-user
REFERENCES
1 N M Simonelli, "Product Design and Human Factors Diversity: What You See Is What You
Get," in Ergonomics: Harness the Power of Human Factors in Your Business, E T Klemmer
(ed.), Ablex, Norwood, NJ, 1989
2 W E Baker, "Human Factors, Ergonomics, and Usability: Principals and Practice," in
Ergon-omics: Harness the Power of Human Factors in Your Business, E T Klemmer (ed.), Ablex,
Norwood, NJ, 1989
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